1. Field of the Invention
The present invention relates to pixel resolution converting circuits capable of extending the pixel resolution and to image display devices using the same.
2. Description of the Related Art
As display devices of personal computers and the like are enlarged and high definition display devices are developed, image display devices capable of converting resolution are becoming widely used. In such image display devices, a video graphics array (VGA) (640xc3x97480 dots) input signal is enlarged and displayed on a super extended graphics array (SXGA) (1280xc3x971024 dots) display area using a general horizontal/vertical doubling method for horizontally and vertically doubling the size of the input signal. In this conversion method, data for one original pixel is applied unchanged to four pixels by horizontally and vertically doubling the original pixel.
FIG. 10 shows the conventional horizontal/vertical doubling conversion method. When data for four original pixels A, B, C, and D are horizontally and vertically doubled and converted into sixteen pixels, each data of the original pixels A, B, C, and D is applied unchanged to four-pixel data obtained by the horizontal/vertical doubling conversion. In practice, four pixels are regarded as one pixel, and display is performed in this way.
Development of display devices of personal computers and the like progressed by realizing large-screen, high-definition display devices. In other words, information to be displayed has been increased, whereas information per unit area in a display area has remained unchanged. When the conventional doubling conversion method is employed to enlarge and display data, information per unit area in the display area is reduced to half, and the density of information in the display area is thereby reduced. This generates jagged edges (xe2x80x9cjaggiesxe2x80x9d) when a character is displayed on such a display device. As a result, image quality is significantly degraded.
FIG. 11 shows an example of an image before the image is enlarged. FIG. 12 shows an example of the same image after the conventional doubling conversion is performed. Referring to FIG. 11, the jaggies in the contours of characters are relatively unnoticeable. However, in FIG. 12, the jagged contours in curved portions of the characters become noticeable. It can be concluded that image quality is degraded by reduction in the density of displayed information.
Accordingly, it is an object of the present invention to provide a pixel resolution converting circuit for horizontally and vertically doubling the pixel resolution and for preventing degradation of image quality due to reduction in the density of displayed information.
According to an aspect of the present invention, the foregoing objects are achieved through the provision of a pixel resolution converting circuit. The pixel resolution converting circuit includes a data array pattern comparing unit for binarizing an input video signal. The data array pattern comparing unit compares a 3-by-3 (nine) pixel array pattern of input image data, including a pixel to be converted and eight pixels vertically, horizontally, and diagonally surrounding the pixel to be converted, and a specific array pattern selected from all possible array patterns formed by combinations of 3-by-3 (nine) pixel binary image data. As a result, it is determined whether the array pattern of the input image data matches the specific array pattern. When the array pattern of the input image data matches the specific array pattern, an enlarged image data generating unit applies image data differing from that of the pixel to be converted to part of image data corresponding to four pixels obtained by vertically and horizontally doubling the pixel to be converted. When the array pattern of the input image data does not match the specific array pattern, the same image data as that of the pixel to be converted is applied to the image data corresponding to all four pixels.
With this arrangement, the image data information about the pixel to be converted and about the surrounding eight pixels is reflected in the image data of the four pixels obtained by enlargement of the pixel to be converted. Based on comparison between the pattern of the nine-pixel image data and the specific pattern, when it is determined that the image forms part of the contour in the diagonal direction, the image data differing from that of the pixel to be converted is applied to part of the image data of the four pixels. Accordingly, the jagged portions in the contour in the diagonal direction can be minimized, thus preventing image quality from being degraded by enlargement.
Preferably, the specific array pattern includes an array pattern in which the image data of the pixel to be converted differs from image data of two pixels adjacent to the pixel to be converted and diagonally adjacent to each other. In such a case, it is preferable that the enlarged image data generating unit differentiate, among the image data of the four pixels to be generated, only image data corresponding to a position adjacent to both pixels having the different image data from the image data of the pixel to be converted.
With this arrangement, when the array pattern of the input image data matches the specific array pattern, it is possible to conclude that the pixel to be converted forms, for example, part of the contour in the diagonal direction. Based on the matched specific array pattern, it is possible to specify the pixel, among the four pixels obtained by vertically and horizontally doubling the pixel to be converted, to which the image data differing from that of the pixel to be converted is to be applied. This minimizes the jagged portions in the contour in the diagonal direction, and thereby prevents image quality from being degraded by enlargement.
Among the image data of the eight pixels surrounding the pixel to be converted, the specific array pattern may include any one of an array pattern in which the number of pixels having the image data differing from that of the pixel to be converted is three, there being at least one pair of adjacent pixels having the different image data, an array pattern in which the number of pixels having the image data differing from that of the pixel to be converted is four, there being two or more pairs of adjacent pixels having the different image data, and an array pattern in which the number of pixels having the image data differing from that of the pixel to be converted is fives there being three or more pairs of adjacent pixels having the different image data. In such a case, it is preferable that the enlarged image data generating unit differentiate, among the image data of the four pixels to be generated, only image data corresponding to a position adjacent to the two pixels adjacent to the pixel to be converted, diagonally adjacent to each other and having the different image data from the image data of the pixel to be converted.
With this arrangement, when the pixel to be converted forms part of the contour in the diagonal direction, the image data differing from that of the pixel to be converted is not easily applied to part of the image data corresponding to the four pixels obtained by vertically and horizontally doubling the pixel to be converted. Hence, image quality is prevented from being degraded by enlargement.
When the specific array pattern is a pattern in which, among the image data of the eight pixels surrounding the pixel to be converted, the number of pixels having image data differing from that of the pixel to be converted is three, there being two pairs of adjacent pixels having the different image data, and when the position of the pixel to be converted is in an even column and an even row or in an odd column and an odd row, it is preferable that the enlarged image data generating unit differentiate, among the image data of the four pixels to be generated, only image data corresponding to a position adjacent to both sets of pixels having the different image data from the image data of the pixel to be converted.
With this arrangement, when the pixel to be converted forms part of the contour in the continuous diagonal direction, the image data differing from that of the pixel to be converted is not easily applied to part of the image data corresponding to the four pixels obtained by vertically and horizontally doubling the pixel to be converted. Hence, image quality is prevented from being degraded by enlargement.
According to another aspect of the present invention, there is provided an image display device including the above-described pixel resolution converting circuit. According to the image display device, it is possible to perform enlarged display in which a displayed image is vertically and horizontally doubled without degrading image quality.